Automobile engine cooling systems contain a variety of metals, including copper, solder, brass, steel, cast iron and aluminum. The possibility of corrosive attack on such metals is high, due to the presence of various ions as well as the high temperatures, pressures, and flow rates found in such cooling systems. The presence of corrosion products within the cooling system can interfere with heat transfer from the engine combustion chambers, and may subsequently cause engine overheating and engine component failure due to excess metal temperatures.
To prevent these problems, a variety of organic and inorganic compositions have been employed as corrosion inhibitors in engine coolant formulations. Illustrative examples of corrosion inhibitors used in engine coolant formulations include silicates, phosphates, organic acids and their salts, azole type compounds, molybdenum, nitrates, nitrites, borates, and the like, as well as combinations thereof.
However, many engine coolant formulations experience a variety of problems commonly attributed to the presence of corrosion inhibitors. Coolants are often provided in the form of concentrates that must be diluted with water prior to use in an automobile engine cooling system.
In some cases, engine coolant concentrates exhibit instability issues after extended warehouse or shelf storage. One common manifestation of storage instability in a coolant concentrate is inhibitor fallout in the form of precipitates. Corrosion inhibitors that are no longer part of a homogenous coolant concentrate will be unavailable in the diluted coolant. A diluted coolant made from an unstable concentrate will thus provide an engine with less corrosion protection.
Another problem encountered with engine coolant concentrates involves the water used for dilution. In many areas the only water available for such use is hard water, or water that contains appreciable levels of dissolved salts. Hardness of water is a function of the concentration of dissolved calcium and magnesium salts contained in the water, and is usually expressed in terms of a concentration (ppm) as CaCO3 Total Hardness. Hard water as used herein refers to water having greater than 150 ppm CaCO3 total hardness. In many cases, the use of hard water for the dilution of coolant concentrates results in a coolant that has adverse effects upon the overall cooling system.
For example, EP 0 245 557 B1 discloses that the use of hard water to dilute antifreeze/coolant formulations containing alkali metal silicate and borate corrosion inhibitors causes the formation of insoluble alkali earth metal silicate floes which precipitate from the antifreeze-water solution. The resulting metal silicate floes are said to be calcium and/or magnesium silicate salts that adversely affect the cooling system for several reasons. First, since the precipitates are alkali earth metal silicate floes, a rapid deletion of silicate in solution occurs; thus the corrosion-inhibiting properties of the formulation are depleted. Moreover, the precipitating solids can eventually plug the passages of the engine cooling system. Second, the formation of hard water scale is undesirable because it can interfere with heat transfer from the engine combustion chambers, and subsequently may cause engine overheating and engine component failure due to excess metal temperatures. EP 0 245 557 B1 discloses the use of phosphino polycarboxylic acid/polycarboxylate compositions, or mixtures thereof as stabilizers to prevent the precipitation of insoluble alkali earth metal silicate and borate corrosion inhibitors where said formulations are diluted with hard water.
However, EP 0 245 557 B1 is limited to the prevention of hard water salts in coolants having only certain corrosion inhibitors. Moreover, none of the prior art has simultaneously resolved the dual problems of coolant concentrate storage stability and the formation of hard water salt formation upon dilution of the concentrate with hard water.
Accordingly, there continues to be a need for the stabilization of coolant concentrates for internal combustion engines.
More particularly, there continues to be a need for methods and compositions directed toward the prevention of the formation of hard water salts upon dilution of engine coolant concentrates with hard water.
Most particularly, there continues to be a need for methods and compositions directed toward the simultaneous stabilization of coolant concentrates and the prevention of hard water salt formation upon dilution of a stabilized engine coolant concentrate with hard water.